Spacecraft structures require the use of advanced lightweight and stiff composite materials in their design to meet the projected weight efficiencies of some current and most future space missions. Unfortunately, these lightweight composites, unlike bolted metallic structures, have very little inherent damping or vibration dissipation characteristics. Thus, due to their light weight and low damping, many structural subsystems with their instruments and electronic payloads, may be subjected to dangerously high vibration levels which compromise their functionality. Of particular interest here are instruments mounted on precision kinematic mounts (KM). Due to their construction techniques, these KM's have very little inherent damping, thus accentuating instrument vibration environment during flight. These environmental effects are brought about during powered flight and pyrotechnic separation/release events. In fact, 14% of spacecraft launches through 1984 (600 launches) suffered vibration/shock related failures. Of these failures, 50% resulted in catastrophic mission loss.
Currently, there are on-going efforts to define graphite structure modifications which lower the overall level of vibration response throughout spacecraft structures. Test and analysis results from a number of space projects using constructions of lightweight graphite composites indicate that the level of reduction likely to be achieved may not be sufficient to bring already developed instruments within their design levels. The need thus arises to identify and make ready for development additional vibration reduction techniques for instruments should the spacecraft structure reduction be proven to be insufficient. In FIG. 1, the instrument 10 is represented by a rectangular solid depicted by broken lines. The instrument 10 is supported by six small precision ground flat pads 12, 14, 16, 18, 20, 22 which only resist loads perpendicular to their plane (individually, they cannot resist bending moments). Under gravity, the three pads 12, 14, 16 support the weight of the instrument 10, i.e., they provide restraint in the z direction. In addition, they restrain the instrument 10 against rotations along the x and y axes. Pads 18, 20 restrain the instrument 10 against translation along the y axis and rotation along the z axis. Finally, pad 22 restrains it against translation along the x axis.
In practice however, it is very difficult to design a linear system of supports which will only provide restraints against translations and none in rotation (i.e. bending action). Conventional designs of three kinematic mounts are depicted in FIGS. 2A-2C. The three mounts are denoted by 24, 30 and 36 in FIGS. 2A-2C, respectively. They comprise a collection of bars 30, 32, 34, 38, 40, 42, 44 attached together. The mount 24 (FIG. 2A) is designed to restrain the instrument predominantly in the axial direction along the longitudinal axis of bar 30, as shown by the arrow 25. At the top and bottom of bar 30, notches 26, 28 have been machined to simulate hinge action, and thus minimize restrains against lateral translations and rotations along three axes. In like manner, mounts 30 (FIG. 2B) and 36 (FIG. 2C) are designed to provide translation restraints predominantly in two and three directions as shown by arrows 31 and 37, respectively. Instruments have been mounted to spacecraft via conventional arrangements of mounts 24, 30 and 36. For a given instrument, particular performance requirements are formulated that specify the maximum values of stiffness the extra restraints can have, which are in excess of the six required for an ideal kinematic mount.
Kinematic mounts, such as those shown in FIG. 2 have met with limited success. Even though these mounts are designed to safely carry the launch loads, the designs have no provisions to minimize loads transmitted to the instrument 10. In particular, the six suspension modes introduced by the mounts are expected to have very little damping, thus amplifying flight loads to the mounted instrument 10.